This invention relates generally to an electrophotographic printing machine, and more particularly concerns an apparatus for assisting in the manual placement of successive original documents onto the platen thereof.
In the process of electrophotographic printing, for example, as disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942, a photosensitive element having a photoconductive insulating layer is charged to a substantially uniform potential in order to sensitize its surface. The charged photoconductive surface is then exposed to a flowing light image of the original document being reproduced. Exposing the charged photoconductive surface to the light selectively dissipates the charge in the irradiated areas in accordance with the intensity of radiation transmitted thereto. This records an electrostatic latent image of the original document on the photoconductive surface. The electrostatic latent image is developed by bringing a developer mix of carrier granules and toner particles into contact therewith. The toner particles and carrier granules are selected such that the toner particles have the appropriate charge relative to the electrostatic latent image recorded on the photoconductive surface. When the developer mix is brought into contact with the electrostatic latent image, the greater attractive force thereof causes the toner particles to be attracted from the carrier granules to the electrostatic latent image. The developed toner powder image is then transferred to a sheet of support material, such as plain paper, to which it may be permanently affixed by the suitable application of heat thereto.
In electrophotographic printing, the original document is manually placed upon the exposure platen located at the top of the printing machine. Thereafter, the optical system forms a light image of the original document which is projected onto the charged photoconductive surface.
Document copying, particularly for high speed electrophotographic printing machines, requires more rapid handling of the original document being reproduced. Hereinbefore, it is known in the art to attach a document feeder to the electrophotographic printing machine when a large number of discrete documents are to be copied. The document feeder transports the original documents in sequence to the exposure platen, actuates the electrophotographic printing machine to reproduce the original documents, and then advances the original document to an output tray. By way of example, U.S. Pat. No. 3,499,710 issued to Sahley in 1967, describes one such type of document feeder.
The document handling art is well developed and includes numerous commercial products which provide for automatically advancing successive original documents onto the platen of an electrophotographic printing machine and for removing them thereafter. Exemplary of the numerous patents teaching various features of automatic document handling are U.S. Pat. No. 1,894,004, issued to Rose in 1933; U.S. Pat. No. 3,062,110, issued to Shepardson et al. in 1962; U.S. Pat. No. 3,136,207, issued to Flad et al. in 1964; U.S. Pat. No. 3,416,860, issued to Mihojevich et al. in 1968; U.S. Pat. No. 3,506,257, issued to Sackler et al. in 1970; U.S. Pat. No. 3,674,363, issued to Baller et al. in 1972; and U.S. Pat. No. 3,726,589, issued to Difulvio et al. in 1973. Other exemplary patents are discussed in co-pending U.S. application Ser. No. 449,307 filed in 1974.
Although numerous automatic prior art devices have been developed in order to obviate the foregoing types of problems, it is highly desirable to develop a relatively simple, inexpensive device which facilitates manual feeding of original documents onto a platen of an electrophotographic printing machine.
Accordingly, it is a primary object of the present invention to improve the manual placement of original documents on the platen of an electrophotographic printing machine.